Dan uses Windows XP and is worried about security once Microsoft ends support for it on April 8th. Leo says that there will only be two more security patch Tuesdays between now and April 8th and once that's done, XP will no longer be supported. Leo says that once that happens, all XP users should pull their XP computers off the Internet completely. There are bad guys who collect flaws and exploits and take advantage of holes in the system. One such nasty thing is Cryptolocker. After April 8th, Leo expects an explosion of Windows targeted viruses, and when there's a flaw in one version, it can affect all versions if they aren't updated.
Dan could possibly put Windows Vista on it, and that's better than nothing. Windows 7 could be workable as well. He could also choose Linux instead. It's open source and free. Leo recommends XUbuntu or Darn Small Linux. He'd have a browser, email, and even have access to some Windows apps. Or, he could buy a new computer and only spend around $400-500.